It looks like a dry/crusty and whitish-grey. I did not dust the crickets today. He gets phosphorus free Rep-Cal with Calcium and Vitamin D on Tuesdays and Fridays, Herptivite on Mondays and Thursdays, and Miner-All 0 on Wednesdays and Saturdays. He is about 3 months old and gets about 8 small crickets a day.
I don't think you should worry.
Maybe reduce the vitamins (not the calcium) to twice a month.
Chameleons excrete excess salts and minerals from their nasal passages.
Give him a good misting and he'll scrape it off himself.
This was happening to me a lot until I adjusted the frequency of vitamins.